It is not at all coincidental. The graph is a total percentage graph. All the lines affect all other lines on the graph. If one rises then others must drop to maintain 100% total. What this does not tell you is if the total windows users dropped, or stayed the same or even if they also grew. Only that relative to Linux the total percentage of windows users dropped.
This could be because a lot of people use Windows and the few niches that do use Linux were less affected by events then the total population. Or that there was a sudden influx of requests from Linux systems for some abnormal reason (like an automated ddos attack).
It is not at all coincidental. The graph is a total percentage graph. All the lines affect all other lines on the graph. If one rises then others must drop to maintain 100% total. What this does not tell you is if the total windows users dropped, or stayed the same or even if they also grew. Only that relative to Linux the total percentage of windows users dropped.
This could be because a lot of people use Windows and the few niches that do use Linux were less affected by events then the total population. Or that there was a sudden influx of requests from Linux systems for some abnormal reason (like an automated ddos attack).